If your PS4 controller is flashing red, it could be due to a few different reasons. Here are a few things you can try to troubleshoot the issue:
Charge the controller: If the controller's battery is low, it may flash red to indicate that it needs to be charged. Try plugging in the controller and see if the red flashing stops.
Restart the controller: Sometimes, a simple restart can fix a variety of issues. To restart your controller, hold down the PS button and the Share button simultaneously for a few seconds until the controller turns off. Then, press the PS button to turn it back on.
Restart the PS4: If restarting the controller doesn't help, try restarting the console itself. To do this, turn off the PS4 by holding down the power button until it beeps twice. Then, unplug the console from the wall outlet and wait 30 seconds before plugging it back in and turning it on.
Check for updates: If the issue persists, it's possible that there is a software issue causing the problem. Check for updates to the controller's firmware and the PS4's system software to see if there are any available updates that could fix the issue.
If none of these steps help, it's possible that there is a hardware issue with the controller. In this case, you may need to contact Sony for further assistance or consider purchasing a new controller.